1. Field of the Invention
The present invention relates to a suspension-type line arrester. More particularly, this invention pertains to a suspension-type line arrester which grounds the surge current generated by lightning strike in transmission lines. The line arrester also promptly cuts off the follow current to prevent ground faults.
2. Description of the Related Art
Generally, surge absorbing devices are provided on transmission lines to absorb any switching surge currents generated by opening or closing of the circuit breaker and any lightning surge currents generated by a lightning strike. Surge absorbing devices prevent ground faults. Conventional arresters do not make suitable surge absorbing devices for transmission lines, because their structure have limited endurance for the line load.
If a conventional arrester is provided on transmission lines, it influences the complex design of the transmission tower and the insulating devices which support the transmission lines. Therefore, a suspension-type line arrester has been proposed for arresting, insulating and supporting transmission lines.
The body of the proposed line arrester has an integrally formed head and shed structure. The shed is formed about the head. A metal pin within the head. A metal cap is installed at the top of the head. The pin and the cap are aligned along the center axis of the insulator body. They are insulated from each other by the insulator body. Bore holes are constructed within the shed. Several resistors having nonlinear varistor voltage-current characteristics are accommodated in each bore hole.
A conductive seal is provided at each vertical end of the bore hole. The resistors are supported within each bore hole by the top and bottom seals. Each top seal is connected to the cap by a connector, and each bottom seal is connected to the pin by a wire.
The pin is a ball type pin. Therefore, the pin base has a larger diameter than that of the pin body. The cap is a socket type cap with an opening formed on the top portion of the cap. The opening opens to the side and therefore, the pin base of the adjoining insulator can be horizontally inserted into the opening.
Once the pin base of a first insulator is engaged with the opening of the cap of a second insulator, the two insulators can not be vertically separated from each other. An insulator string is constructed by linking several insulators. The transmission lines are suspended from the tower by the insulator strings.
In the event of a lightning strike, a large surge current flows from a tower to the transmission lines or from a transmission line to a tower by way of insulator strings. In each insulator, the surge current flows through the route sequentially set by a pin, a wire, a bottom seal, resistors, a top seal, a connector and a cap.
Conventional insulators can rotate relative to their adjacent (upper and lower) insulators around the center axis of the insulator string. Accordingly, even though each insulator is mounted so that resistors of the vertically linked insulators are aligned in a vertical direction, swaying in the transmission lines can cause misalignments between the resistors of the upper insulator and the resistors of the lower insulator.
When the energy of the surge is over the capacity of the resistor, the resistors break down due to the excess surge current and become conductive. Then, an arc discharge will occur directly between the resistors of the upper insulator and the resistors of the lower insulator. If the resistors are misaligned, the course of the arc discharges are in a zigzag manner along the insulator string. Such an arc discharge pattern damages the surface of the sheds of the insulators.